1. Field of the Invention
This invention relates to a process for the production of a propellant additive, and is more particularly directed to an aqueous process for the production of glycidyl azide polymer (GAP) from polyepichlorohydrin (PECH).
2. Description of the Prior Art
The direct introduction of the azido group by nucleophilic displacement with azide ion constitutes the most convenient and general synthesis of aliphatic azides. A wide range of leaving groups has been employed in the reaction, e.g., sulfate, nitro, nitrate, phenylazo, and iodoxy, but p-toleunesulfonyl, methanesulfonyl, and halogeno derivatives are the most frequently used.
Prior to the use of dipolar aprotic solvents for these reactions, the general procedure involved interactions of the alkyl substrate with sodium azide in aqueous alcohol. Sealed tubes and a complicated work-up procedure including the separation of azeotropic mixtures were required, and in addition the facility of the reaction depended critically on the nature of the sodium azide employed. This situation existed until 1957 when Lieber, Chao, and Rao demonstrated the advantages to be gained from using high-boiling solvents such as the monalkyl ethers of diethylene glycol. (Lieber, E., T. S. Chao, and C. Rao, J. Org. Chem., 22, 238 (1957). This modification, which obviated the use of sealed tubes and the prior activation of sodium azide, enabled higher yields to be achieved and work-up procedures were simplified since azeotropic mixtures were not formed. Dipolar aprotic solvents are even more efficacious and dimethylsulfoxide (Jones, D. N., Chem. Ind. (London), 179 (1962) and dimethylformamide (Smolinsky, G., J. Am. Chem. Soc., 83, 4483 (1961) are now used routinely as media for azide substitution reactions.
As previously noted, dipolar aprotic solvents such as dimethylformamide are efficient solvents for the synthesis of azido compounds. However, they are expensive and they cause problems in the synthesis of polymeric azides. The principal problem associated with the use of these solvents is the difficulty in their quantitative removal from the polymeric product. The polymer tends to hold on to the solvent and multiple water washings are required to remove the solvent. Furthermore, such systems tend to emulsify and make separation of the layers very difficult, causing loss of product. Consequently, very long work-up times are required to isolate the solvent-free polymer.